1. Field of the Invention
The present invention relates to a method and apparatus for manufacturing semiconductor devices in which ruthenium films or ruthenium oxide films are formed on a substrate.
2. Description of the Prior Art
The formation of thin ruthenium films, major candidates of next generation""s DRAM electrodes, using a sputtering process, has been technically established and frequently employed at the research level. However, the formation of thin films by the use of sputtering is defective in the ability of covering stepped portions (hereinafter called xe2x80x9cstep coveragexe2x80x9d), and hence a thermal CVD method having a superior step coverage is preferred for mass production processes and has been actively developed.
In the thermal CVD method, the film-forming raw material is generally in the form of a liquid of an organic metal, a solution with a powder of an organic metal dissolved in a solvent or the like, these materials being vaporized by means of a vaporizer or bubbling and supplied to a substrate. Here, bisethyl-cyclopentadienyl-ruthenium (Ru(C2H5C5H4)2) is referred to as such a raw material.
In general, a ruthenium film or a ruthenium oxide film is formed on an upper portion of an interlayer insulation film such as a silicon oxide film, a silicon nitride film, etc., or on an upper portion of a barrier metal layer formed of a metal such as TiN, TiO2, WN, etc. However, with such an underlayer, there is a deficiency in that a delay in deposition would be caused in cases where ruthenium films or ruthenium oxide films are formed by means of a thermal CVD method while particularly using bisethyl-cyclopentadienyl-ruthenium and oxygen as raw materials. On the other hand, the step coverage in the case of using above-mentioned raw materials is good at a film-forming temperature range of about 300xc2x0 C. (i.e., 290xc2x0 C. to 330xc2x0 C.), but at this temperature range, a delay in deposition will be caused, taking time until a thin film of a desired thickness has been formed. Thus, this is not suitable for mass production. Moreover, when the film formation is performed at a temperature higher than 330xc2x0 C., the time for the film formation can be shortened, but on the contrary, there arises a deficiency in that the step coverage is impaired.
On the other hand, in the case where ruthenium films or ruthenium oxide films are formed on a substrate by means of a thermal CVD method, a deposition delay will not be caused even at a temperature as high as about 300xc2x0 C. if a ruthenium film or a ruthenium oxide film is formed in advance on the substrate by the use of a sputtering apparatus. However, this results in a further disadvantage that it is necessary to use two reactors, thus reducing the throughput and increasing the cost of equipment.
Accordingly, the object of the present invention is to provide a method for manufacturing semiconductor devices at low cost, which is excellent in the step coverage and the throughput.
Thus, according to one aspect of the present invention, there is provided a semiconductor manufacturing method including a film-forming process in which ruthenium films or ruthenium oxide films are formed on a substrate by using a gas vaporized from a ruthenium liquid material and an oxygen-containing gas. The film-forming process comprises: an initial film-forming step for initially forming a first thin film of ruthenium or ruthenium oxide on the substrate under first film-forming conditions; and a main film forming step for forming a second thin film of ruthenium or ruthenium oxide on the first thin film under second film-forming conditions different from the first film-forming conditions, the second thin film having a thickness greater than that of the first thin film. With this semiconductor manufacturing method, it is possible to provide semiconductor devices which are excellent in the step coverage, high in throughput, and low in the cost of manufacture.
In a preferred form of the present invention, the initial film-forming step and the main film-forming step are performed continuously in one and the same reaction chamber by means of a thermal CVD method. Thus, semiconductor devices can be manufactured at much lower cost.
In another preferred form of the present invention, the second film-forming conditions in the main film-forming step provide a step coverage better than that of the first film-forming conditions in the initial film-forming step. Thus, semiconductor devices can be manufactured which are excellent in the step coverage, high in throughput, and low in cost.
In a further preferred form of the present invention, the second film-forming conditions in the main film-forming step provides a deposition rate greater than that of the first film-forming conditions in the initial film-forming step. Thus, semiconductor devices can also be manufactured which are excellent in the step coverage, high in throughput, and low in cost.
In a still further preferred form of the present invention, the second film-forming conditions in the main film-forming step provide a film-forming temperature or pressure higher than that of the first film-forming conditions in the initial film-forming step. Thus, in this case, too, semiconductor devices can be manufactured which are excellent in the step coverage, high in throughput, and low in cost.
In a yet further preferred form of the present invention, the second film-forming conditions in the main film-forming step provide a ratio of a flow rate of the oxygen-containing gas to a flow rate of the vaporized ruthenium gas greater than that of the first film-forming conditions in the initial film-forming step. Thus, in this case, too, semiconductor devices can be manufactured which are excellent in the step coverage, high in throughput, and low in cost.
In a further preferred form of the present invention, the first film-forming conditions in the initial film-forming step comprises a film-forming temperature in the range of from 300xc2x0 C. to 350xc2x0 C. and a film-forming pressure in the range of from 667 Pa to 3,999 Pa. Thus, in this case, too, semiconductor devices can be;manufactured which are excellent in the step coverage, high in throughput, and low in cost.
In a further preferred form of the present invention, the ruthenium liquid material comprises bisethyl-cyclopentadienyl-ruthenium.
According to another aspect of the present invention, there is provided a semiconductor manufacturing apparatus comprising: a reaction chamber adapted to accommodate a substrate; a gas feed port through which a raw material gas is supplied to the reaction chamber for forming ruthenium films or ruthenium oxide films on the substrate; and a gas exhaust port through which the raw material gas is exhausted from the reaction chamber; wherein the raw material gas is directed from the gas feed port toward the substrate to initially form thereon a first ruthenium film or a first ruthenium oxide film by means of a thermal CVD method under first film-forming conditions, and subsequently to form a second ruthenium film or a second ruthenium oxide film on an underlayer of the first ruthenium film or the first ruthenium oxide film by means of the thermal CVD method under second film-forming conditions different from the first film-forming conditions, the second ruthenium film or the second ruthenium oxide film having a thickness greater than that of the first ruthenium film or the first ruthenium oxide film. With such an arrangement, it is possible to provide semiconductor devices which are excellent in the step coverage, high in throughput and low in the cost of manufacture.
The above and other objects, features and advantages of the present invention will become more readily apparent to those skilled in the art from the following detailed description of preferred embodiments of the present invention taken in conjunction with the accompanying drawings.